Mmm, when I convert the cbr to a cbz file, is works. But with approx. 44K of cbr files, I do not feel happy when I need to convert them all. Besides that, all comics that I download, are always in cbr format.

Did some further testing. As long as the thumbs.db file is present in the cbr file (even when renamed to something else), I get the 'could not open file' message. Rebuilding the cbr does not help. Removing other files from the cbr (causing a rebuild) does not help. But as soon as the thumbs.db file is removed, the file opens. So for me, there is a clear relation to the thumbs.db file. It might be, that anything other than a jpg file inside a cbr file, causes the same issue. That I did not test.

That is a good question. I am not 100% sure, that is the case. But of all cbr files that I see that are not processed correctly, about 98% has a thums.db file in it. 1% contains both jpg and png files. And the left over 1%, I have no idea what is wrong with them. But, next time I see a cbr with a thumbs.db, I will just recompress it, I check if the issue is solved.

It stops scanning at item 18196. All my books are comic books.
I used the package ubooquity_x64-5.0_1.7.0-1.spk to install ubooquity on the synology. But I cannot find where I can change the memory setting to -Xmx1024m. Do you know where to set/change it in DSM5?
All comics are grouped in a main folder with subfolders per serie. In total i have currently about 2500 subfolders. 

Hi, I have the same issue. When the number of books is small, everything runs fine. But with a large collection, I get outofmemory errors / java heap space. Also, when changing a ubooquity setting, i get the messeage 'server restarting' (in a different format than normal), and then the message, 'server down'. After this message, there is no way i can get it to work normally. I have to uninstall and install the software again, and rebuild the db. And a rebuild of the db takes more than 8 hours, ending with the memory error. 
I run the software on a Synology. And as said, with a small collection of books (less than 8000 or so) everything runs fine, and I realy like it.